Aburaki et al. U.S. Pat. No. 4,406,899 discloses 7-[(Z)-2-methoxyimino-2-(2-aminothiazol-4-yl)acetamido]-3-[(1-methyl-1-pyr rolidinium)methyl]-3-cephem-4-carboxylate in the zwitterion form and mentions corresponding acid addition salts (which are present in the zwitterion form in injectable compositions) and shows that the zwitterion form has broader spectrum activity than ceftazidime and cefotaxime.
However, the aforementioned Aburaki et al. cephalosporins are stable only for a few hours as injectable compositions and the zwitterion form even as a dry powder is unstable at room temperature and loses 30% or more of its activity on storage at elevated temperatures (e.g. 45.degree. C. and above) for even one week.
Crystalline acidic salts, such as H.sub.2 SO.sub.4 salts, of the zwitterion are high temperature stable but are too acidic for intramuscular and intravenous use and somewhat excessive quantities of varied bases and buffering agents are required to obtain physiologically acceptable pH ranges (3.5-7.0) with the acidic salts.